The present invention relates generally to artificial heart valves, and more particularly, is directed to a stented bioprosthetic heart valve.
Diseased heart valves may either be repaired through surgical techniques or replaced with an artificial valve. Although reconstructive surgery has been shown to be superior to valve replacement, it is difficult to perform and is not always possible in every patient. The vast majority of patients have their valves replaced with artificial valves. There are two basic types of artificial valves. The first type of artificial valve, called herein a xe2x80x9cprostheticxe2x80x9d valve, is typically made of metal or a plastic material. The second type of artificial valve, called herein a xe2x80x9cbioprostheticxe2x80x9d valve, comprises a prosthetic device and biological tissue. Both types of valves come in different shapes and diameters depending upon the particular valve being replaced (e.g., mitral, aortic, tricuspid, or pulmonary) and the size of the individual patient""s heart. For example, a typical artificial aortic valve has an orifice opening of approximately 19-29 mm in diameter and a typical artificial mitral valve has an orifice opening of 23-35 mm in diameter.
The bioprosthetic valves comprise a biological valve member which is typically an animal heart valve. The biological valve member is defined by a tubular wall having an approximate thickness of 1.5 mm and three flexible leaflets integrally connected to the tubular wall which converge axially along three commissures. The biological valve member may be a bovine pericardium or a porcine aortic valve which is chemically treated. The porcine aortic valve is generally used for all valve replacements in the human heart. The size of the porcine aortic valve may vary, however, depending on the type of valve being replaced in the patient (e.g., mitral, aortic, tricuspid, or pulmonary) and the size of the individual patient""s heart.
Bioprosthetic valves are divided into two broadly defined classes. The first class of bioprosthetic valves are stented having a frame (or stent) to which the biological valve member is attached. The biological valve members are sutured to the stent which provides support for the valve member in the patient""s body. The stent prevents the biological valve member from collapsing and simplifies the insertion of the valve into the annulus of the patient after excision of the diseased valve. The stented bioprosthetic valves imitate the natural action of heart valves and provide a structure which is relatively compatible with the cardiovascular system.
The second class of bioprosthetic heart valves are stentless and thus do not have a frame. Rather, the biological valve member is sutured to a flexible cloth material. The hemodynamics of a stentless valve more closely approximates that of a natural heart valve. A drawback of a stentless valve, however, is that it is more difficult to implant into the patient than a stented valve. Furthermore, a stentless valve can be collapsed and deformed by the action of the heart because it has no support structure. The action of the heart muscles on this type of valve can fold the valve material and create unexpected stress risers which can eventually lead to failure.
The stented bioprosthetic valves are believed to have important clinical advantages over mechanical non-tissue prosthetic valves. Reports on the use of bioprosthetic valves indicate that the risks of thromboembolism are lower, the need for long-term anticoagulation is minimized, and the nature of occasional valve failure is progressive, thereby permitting elective reoperation under optimal conditions.
Known stented bioprosthetic valves comprise a frame defined by a support rail which is made of either a steel alloy or thermoplastic material, and a plastic wall. The support rail has a circular cross-section and is formed to define three commissure posts supporting the three leaflets of the biological valve member. The plastic wall conforms to the shape of the support rail defined by the three commissure posts providing a rigid support in the lateral direction. The support rails are typically flexible, but not elastic, because the commissure posts are relatively rigid. As the valve leaflets move from open to closed positions, bending stresses occur in the portion of the support rail connecting the commissures. However, the commissure posts themselves do not bend significantly.
The frame is typically covered with a padded, gusseted and porous covering to facilitate attachment, tissue invasion, and encapsulation. A sleeve of porous biocompatible cloth is fitted about the frame and is loosely stitched thereto. Thereafter, a support ring having insert elements which may be portions of a plastic web is positioned outside of the sleeve between each of the commissure posts. The sleeve is trimmed and secured by stitching to the margins of the insert elements. A covering of porous biocompatible cloth is then fitted about the stent, completely enclosing the frame and inserts. The support ring is thus rigidly attached to the frame making the valve inflexible in the lateral direction. A padded suturing rim is formed about the outer periphery of the stent by either folding the cloth upon itself or enclosing an annulus of resilient foam or sponge rubber with the cloth covering.
The cloth layers are typically formed of porous woven or knitted Teflon or Dacron. The insert elements are formed from a sheet or sheets of polyglycol terephthalate (Mylar) although other biocompatible materials such as polypropylene may be used.
The insert elements serve as gussets for increasing the axial dimensions of the stent in the zones between the commissure posts and for providing an attachment surface for the cloth and the biological valve member. Each insert element of the connected series is typically provided with apertures through which stitching is extended during fabrication of the stent.
With the prior art bioprosthetic valves, the biological tissue making up the biological valve member is stitched to the inner wall of the stent. This construction reduces the overall opening through which blood can flow through the valve. The overall thickness of the stented bioprosthetic valve wall is therefore equal to the sum of the thicknesses of the frame wall and the covering mounted thereon which is approximately 1.5 mm (3 mm in cross-section) and the thickness of the tubular wall of the biological valve member which is approximately 1.5 mm (3 mm in cross-section) for a total thickness of approximately 6 mm in cross-section. Thus, with the prior art stented bioprosthetic valves the overall cross-sectional opening of the replaced valve is 6 mm smaller than the patient""s natural heart valve. Accordingly, the blood flowing through the bioprosthetic valve is forced through a smaller area than would ordinary flow through a natural valve thus forcing the heart to work harder to circulate the blood through the patient""s body. Furthermore, this reduced opening has a greater risk of becoming blocked than a healthy natural valve.
Recent efforts have been made to reduce the overall thickness of the valve wall. These efforts have only concentrated on reducing the thickness of the stent wall. However, the thickness of the stent wall can only be reduced so much before the stent loses its structural integrity. No efforts have been made to reduce the thickness component due to the biological valve member.
The present invention is directed to overcoming or at least minimizing some of the problems mentioned above.
In the embodiment of the invention disclosed herein, a supported bioprosthetic heart valve is provided. The valve includes a stent and a biological valve member. The stent has an annular frame defined by a support rail. The support rail is formed to define a triad of axially-projecting circumferentially-spaced commissure posts. Each commissure post has an inverted U-shaped configuration having a rounded upper end and a pair of legs. Each of the pair of legs has an upper end and a lower end. The lower end of each leg merges smoothly with the lower end of a leg of an adjacent commissure post. The biological valve member has an inflow end and an outflow end, defined by a tubular wall and three leaflets, the three leaflets being attached to the tubular wall and axially converging along three commissures. The outflow end of the biological valve member is disposed under the support rail and has a shape which fits the contour of the support rail. A sleeve having an inflow end and an outflow end is fitted around the annular frame. The inflow end of the sleeve is sutured to the inflow end of the biological valve member and the outflow end of the end of the sleeve is sutured to the support rail and the outflow end of the biological valve member.
The bioprosthetic heart valve also includes a suturing cuff which is not rigidly attached to the support ring allowing the valve to expand and contract in the lateral direction. The suturing cuff is formed by wrapping the inflow end of the sleeve around a ring-shaped cushion and suturing the sleeve to itself thus encapsulating the ring-shaped cushion. An inflow support ring may also be encapsulated with the ring-shaped cushion by the sleeve for added support. In another embodiment, the suturing cuff is formed by wrapping the inflow end of the sleeve upon itself and suturing the sleeve in place. In this latter embodiment, neither the ring-shaped cushion nor the inflow support ring are used.